Speech Processing in Dyslexia

The root of dyslexia may be in speech processing, a surprise to researchers. How will this knowledge help treat it?

People speaking the same language produce minute differences in the sounds they make. Most people perceive these differences, which helps them identify the speaker. But people with dyslexia often have problems in this area.

Author of a new study exploring this discrepancy, Tyler Perrachione, explains that "[e]ven though all people who speak a language use the same words, they say those words just a little bit differently from one another--what is called 'phonetics' in linguistics."

The people with dyslexia had a much harder time with the task with English speakers, compared to controls. But with Mandarin, they were virtually no different from controls.

Phonetics looks at the "physical properties" involved with speech. Since people with dyslexia often have problems perceiving these differences, Perrachione and his colleagues theorized that they would also have problems identifying speakers of their native language (English) vs. speakers of Mandarin Chinese.

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They had people with dyslexia and normal Control listen to five cartoon characters with different "voices" so that they would learn to match the speaker with the voice. Later, they were tested on how well they could identify the voices. The people with dyslexia had a much harder time with the task with English speakers, compared to controls. But with Mandarin, they were virtually no different from controls.

The study’s insight comes from its laying out the connection between reading and language processing. "Our results are the first to explicitly link impairment in reading ability to impairment in…processing spoken language," said Perrachione.

How can this research actually help people with dyslexia? It may help educators be more mindful of the difficulties that people with dyslexia have in all types of language processing, particularly speech. "Lots of research has shown that individuals with dyslexia have more trouble understanding speech when there is noise in the background," says Perrachione. "These results suggest that trouble following a specific voice might be part of the cause. Teachers and other educators can be sensitive to this during classroom instruction where noise from other classmates might make it disproportionately difficult for children with dyslexia to follow what is going on in a lesson."

More research will need to explore the connection further, and to develop new methods for treating dyslexia at the earliest possible stage.

Perrachion is a PhD candidate at MIT; the study was published in the July 29, 2011 online issue of Science.